An evaluation of Bosniak's radiological classification of cystic renal masses

OBJECTIVE: To determine the clinical usefulness of Bosniak's classification of cystic renal masses, the differentiation of which remains difficult despite significant advances in diagnostic imaging. PATIENTS AND METHODS: The computed tomography (CT) findings of all histopathologically examined cystic renal masses diagnosed at our institution were analysed retrospectively; 35 patients with cystic renal masses were treated between 1986 and 1998. Tissues surgically removed were examined pathologically and the final diagnosis compared with the preoperative CT category of Bosniak's classification. RESULTS: The histopathological examined showed cystic renal cell carcinoma in 21 patients, a benign renal cyst in 12, haemangiosarcoma in one and transitional cell carcinoma in one. Most of the 35 masses (26, 74%) were found incidentally during evaluation for an unrelated disease or a routine health check. All 11 masses of Bosniak category I were benign and one category II mass was malignant. All 10 masses of category III and 12 of category IV were malignant. CONCLUSIONS: Bosniak's classification is useful for differentiating category I, III and IV cystic renal masses. There were too few samples to allow meaningful conclusions to be drawn for category II renal masses. It is critical to differentiate between complicated cysts of category II and III because of the major implications for prognosis and clinical management.